Interpretive Summary: Globally, genetic diversity of livestock populations is contracting. Knowing the true extent of the contraction is needed to develop effective conservation strategies. To accomplish this goal, pedigree records were obtained for: Duroc, Hampshire, Landrace, and Yorkshire, and Berkshire. Number of registrations peaked in 1990 for all breeds except Berkshire and all have been declining in the current decade. Presently, more than 99% of all pigs are inbred with the majority having inbreeding less than 10%. The range for percent of animals that are more than 25% inbred ranged from 1.16% for Yorkshire to 6.09% for Berkshire. The highest inbreeding for all animals within a breed ranged from 51% for Landrace and 65% for Yorkshire. Generation numbers were computed with the founders defined as having unknown parents, assigned as generation zero. Generations ranged from 17 to 19 per breed with a generation interval ranging from 1.65 yr for Berkshire to 2.21 yr for Yorkshire. Mean inbreeding (%) at generation 17, inbreeding rate of increase per generation, and effective population size were 12.3, 0.0065, and 77 for Berkshire, 11.8, 0.0044, and 113 for Duroc, 6.8, 0.0046, and 109 for Hampshire, 17.9, 0.0067, and 74 for Landrace, and 8.0, 0.0044, and 113 for Yorkshire, respectively. The two breeds with fewest registrations, Berkshire and Landrace, have a higher inbreeding rate and lower effective population sizes; suggesting these breeds need more assertive conservation in order to maintain genetic diversity. This analysis provides a basis for future monitoring of the genetic diversity of pig breeds.

Technical Abstract:
Globally, genetic diversity of livestock populations is contracting. Knowing the true extent of the contraction is needed to develop effective conservation strategies. To accomplish this goal, pedigree records were obtained for: Duroc (n = 878,480), Hampshire (n =744,270), Landrace (n = 126,566), and Yorkshire (n =727,268) from NSR, and Berkshire (n = 116,758 American Berkshire Association). Number of registrations peaked in 1990 for all breeds except Berkshire and all have been declining in the current decade. Presently, more than 99% of all pigs are inbred with the majority having inbreeding less than 10%. The range for percent of animals that are more than 25% inbred ranged from 1.16% for Yorkshire to 6.09% for Berkshire. The highest inbreeding for all animals within a breed ranged from 51% for Landrace and 65% for Yorkshire. Sires were grouped into ten percentiles based on number of great-grandprogeny (GGP); the top percentile for all breeds accounted for more than 75% of all GGP. Sixty percent of all sires produced less than 1% of all GGP, indicating few males are responsible for the majority of future generations, thus narrowing the genetic base. Generation numbers were computed with the founders defined as having unknown parents, assigned as generation zero. Generations ranged from 17 to 19 per breed with a generation interval ranging from 1.65 yr for Berkshire to 2.21 yr for Yorkshire. Mean inbreeding (%) at generation 17, inbreeding rate of increase per generation, and effective population size were 12.3, 0.0065, and 77 for Berkshire, 11.8, 0.0044, and 113 for Duroc, 6.8, 0.0046, and 109 for Hampshire, 17.9, 0.0067, and 74 for Landrace, and 8.0, 0.0044, and 113 for Yorkshire, respectively. The two breeds with fewest registrations, Berkshire and Landrace, have a higher inbreeding rate and lower effective population sizes; these breeds need more aggressive conservation in order to maintain genetic diversity. This analysis provides a basis for future monitoring of the genetic diversity of pig breeds.
Key Words: Genetic diversity, Swine, Inbreeding